Many motor systems with very high reliability requirements require position transducers that have a very low probability for failure. In some cases such as the system shown in the cited U.S. patent application “Actuator and movement linkage system”, the same shaft may be run by more than one processor. Each of these processors is capable of controlling the same motor windings. In the case where a first processor fails, a stand-by processor may take the control. In order reduce the likelihood of failure of a common part, it is advantageous to have electrically separate angular transducer systems with a minimum of common parts.
Most motors have a protruding shaft in one end of the rotor and a bearing in the other, behind which position transducers having small diameters can be assembled. Some motor systems have a large shaft or a bore through the rotor that is occupied by cables, pipes for cooling fluid, transmission shafts that carry torque from an internal combustion engine on one side of the motor to a gears on the other side of the motor or, as shown in the cited International patent application No. WO 2004/034550, an actuator roller screw. Many position transducer principles that perform well for small diameters becomes less attractive when designed to permit a large diameter shaft.
Position transducers having high resolutions are often designed for limited humidity and have reduced or no performance if contaminated by products such as condensed water, oil, grease or particles from wear in friction brakes or gears.
Many position transducers have small air gaps which can be filled with condensed water that in vehicles and aircraft may freeze. Moving motors including transducers in which ice is formed in thin air gaps may cause the parts of the transducers to break or be distorted or be turned away from their calibrated position.
In the case where there is a need to know how many turns the rotor has moved, in most industrial motors space is available for mechanic devices of small diameters that can use cog wheel gears to record a limited number of turns. Industry standard devices can often record movements in within 2048 full turns. Such devices scale badly and may easily break if forced to move with frozen water in the mechanic parts.